Grease Pencil in 2.8 can you link or reuse mouth shapes
maybe you've already found the way, but just in case: If I understood it well, yes. You have to create the phonemes as a grease pencil object whit all shapes as a frames in a separate blend file. Link the mouth object via "file> link>object" in the destination file. place your instance and edit frame phoneme order as you want. Go back to the original file whenever you want to edit one of the phonemes. Save and the edited shapes would update.